Transcript Aula12-09-Particle Size

Nanoparticles Characterization:
Measurement of the particles
size by the PCS technique
MSc. Priscyla D. Marcato
Dr. Nelson Durán
Principle of Measurement
• If the particles or molecules are illuminated with a
laser, the intensity of the scattered light fluctuates at
a rate that is dependent upon the size of the particles
• Analysis of these intensity fluctuations yields the
velocity of the Brownian motion and hence the
particle size using the Stokes-Einstein relationship.
Brownian Motion
Particles, emulsions and
molecules in suspension
undergo Brownian motion.
This is the motion induced by the
bombardment by solvent
molecules that themselves are
moving due to their thermal
energy
Temperature and viscosity must
be known
Stokes-Einstein relationship
The velocity of the Brownian motion is defined by a
property known as the translational diffusion
coefficient (usually given the symbol, D).
No spherical particles
Hydrodynamic diameter is calculated based on the
equivalent sphere with the same diffusion coefficient
He-Ne Laser
 = 633 nm
Zetasizer Nano ZS
Malvern
Brownian motion and scattering
Intensity of the scattered light
fluctuates
Intensity of the scattered light
fluctuates
Small particles- noisy
curve
Large particles- smooth
curve
Determining particle size
Determined autocorrelation function
Depend
Correlation function Correlograms
Correlogram from a
sample containing
large particles
Correlogram from a
sample containing
small particles
Low
concentration
High
concentration
turbidity is linear with
concentration
Particles are so close together
that the scattered radiation is
re-scattered by other particles.
Optical
arrangement
in 173°
backscatter
detection
Information
Size by:
- Intensity
I  d6
Rayleigh Scattering
(For nanoparticles less than d =λ/10 or around 60nm
the scattering will be equal in all
Directions-isotropic)
80 nm
8 nm
This particles will scatter 106 (one million) times
more light than the small particle (8 nm)
The contribution to the total light scattered by the
small particles will be extremely small
8
80
By the Mie theory is possible convert intensity
distribution into volume
- Volume

- Number
 d1
d3
V= 4r3
r = d/2
V= 4(d/2)3 = 4d3
8
Two population of spherical nanoparticles :
5 nm and 50 nm
(in equal number)
Which of these distributions should I use?
d(intensity) > d(volume) > d(number)
Direct determination of the number-weighted
mean radius and polydispersity from dynamic
light-scattering data
Philipus et al., Applied Optics, 45, 2209 (2006)
We
find
that
converting
intensity-weighted
distributions is not always reliable, especially when
the polydispersity of the sample is large.
Zeta Potential